Small electrical unit with molded ceramic coating



Jan. 11, 1966 BERKELHAMER 3,229,237

SMALL ELECTRICAL UNIT WITH MOLDED CERAMIC COATING Filed Feb. 9, 1962 INVENTOR.

United States Patent 3,229,237 SMALL ELECTRICAL UNIT WITH MOLDED CERAMIC COATING Louis H. Berkellamer, Glencoe, Ill., assignor, by mesne assignments, to Consolidated Electronics Industries Corp., New York, N.Y., a corporation of Delaware Filed Feb. 9, 1962, Ser. No. 172,329 1 Claim. (Cl. 338-266) This invention relates generally to small electrical units and especially to insulating coatings for .such units.

According to modern practice, numerous types of small electrical units are fabricated to comprise a relatively rigid core, an electrical element disposed on the core for support, and an insulating coating covering the electrical element and the core. The three most common types of insulating coverings are (l) resinous plastic materials, including varnishes and molded bodies, (2) glass sleeves or tubes, and (3) vitreous enamel coatings applied by either the dip or the spray process. While resinous plastic coatings possess certain advantages, the principal difiiculty with these coatings resides in their inflammability, actual ignition being capable of occurring as upon a momentary, high overload of the electrical unit. When glass sleeves or tubes are employed as external insulation, on the other hand, damage to the seal at the electrical lead exposes the entire electrical element to the atmosphere, not just a small part of it. Furthermore, glass sleeves or tubes must be arranged to fit loosely over the core and over the electrical unit in order to facilitate assembly; and the resultant air space prevents good heat dissipaton from the unit in use whereby to require a lower wattage rating to be applied to the unit than might otherwise be necessary.

Although vitreous enamel coatings do not possess the above-described disadvantages, the proper application of coatings of this nature require numerous manufacturing Operations including substantial amounts of hand labor. There i s a need for much careful inspection, reworking and cleaning; and the units are commonly rotated in the firing furnace in order to reduce run-off of the enamel in its fluid state. Furthermore, the electrical elements can move due to flow of the enamel during fi-ring; and there is the problem of the coating burning through at thin spots. In addition, the fluidity of the enamel during the firing step prevents controlling of the gross shape of 'the unit with any degree of precision. Moreover, when the enamel slp is applied by spraying .rather than by dipping, the overspray must be recovered and reprocessed in order to make the operation economical.

Therefore, a general object of the present invention is to provide a new and improved electrical unit which overcomes the limitations of the prior art.

Another object of the invention is to provide an electrical unit which possesses a precisely controlled overall shape and which is completely non-flammable.

Still another object of the invention is to provide incombustible electrical units having a highly uniform insulation value from unit to unit.

And still another object of the invention is to provide an electrical unit which achieves rapid dissipaton of heat.

A further object of the invention is to provide an electrical unit which is amenable to automated assembly into electrical systems and circuitry.

Additional objects and features of the invention pertain to the particular structure, materials and arrangements whereby the above objects are attained.

An electrical unit in accord with the invention includes a ceramic core; a metallic wire element wound on the core; and a molded, vitreous body of ceramic material coating the exposed portions of the surface of the core 3,229,237 Patented Jan. 11, 1966 "ice and of the element, the body of ceramic material comprising both glassy and non-glassy particles, the glassy particles being fused together at Contacting surfaces whereby the body forms a monolithic envelope.

In order that the principle of the invention may be readily understood, a single embodiment thereof applied to an axial lead resistor, but to which the application is not to be restricted, is shown in the accompanying drawing wherein:

FIG. 1 is a .perspective View of an aXial lead resistor ncorporating an insulating coating in accord with the invention; and

FIG. 2 is an enlarged view taken through the section 2-2 of FIGjl and illustrating the character of the insulating coating.

Referring now in detail to the drawing, an electrical unit indicated generally by the numeral 10 will be seen to comprise an axial lead resistor. However, the unit 10 could as well comprise a rheostat or other electrical unit for purposes of the present application. The electrical unit 10 specifically includes a rigid, ceramic core 12; and in one specific embodiment of the invention, the core 12 has been fashioned from the mineral substance known as sta-tite. When the electrical unit of the invention takes the form of an axial lead resistor, the core 12 is fabricated as a cylinder and conductive metal end caps 14 are assembled to the core 12 in a friction fit. In accordance with conventional practice, lead wires 16 are mechanically and electrically connected to the end caps 14 to extend along the axis of the cylindrical core 12.

The electrical unit 10 additionally includes an electrical element 18 disposed on the core 12; and conventionally, the element 18 takes the form of a metallic wire element which is helically wound on the core between the end caps and which is both mechanically and electrically connected to the end caps. When the electrical element 18 is -so disposed on the core 12, :portions of the surface of the core are covered with the electrical element and other portions are left exposed.

In compliance with -an important feature of the present invention, a vitreous body 20 of ceramic material -is applied to the electrical unit as a coating. This coating is, in accordance with the invention, molded; and during the process of its manufacture, the electrical unit is subjected to temperatures suiciently high to cause the glassy ceramic materials contained within the body 20 to fuse, the body 20 thereby forming a monolithic envelope completely covering both the end caps 14 and the exposed portions of the surfaces of core 12 and electrical element 18.

With reference to FIG. 2, the body 20 of ceramic material will be seen to comprise particles of non-glassy ceramic material 22 bound up in a matrix 'of fused glassy ceramic material 24. The glassy ceramic material originally exists as separate particles intermixed with the particles of non-glassy ceramic material; and upon subjection to appropriate temperatures, the particles of glassy ceramic material fuse together at Contacting interfaces whereby to form the glassy matrix 24.

Because the vitreous body 20 is molded, the external shape and dimension of the electrical unit 10 can be precisely controlled, thus insuring uniform insulation value from one unit to the next and thus permitting automation of assembly of the unit 10 with other Components in an electrical device or appliance. Moreover, molding of the vitreous body 20 nsures intimate contact between the body and the exposed -surfaces of both the core 12 and the electrical element 18 whereby to insure positive positioning of the electrical element relative to the core and whereby to insure rapid dissipaton of heat generated by the unit in use.

The specific example heren shown and described should be considered as illustrative only. Various changes may occur to those skilled in the art; and such changes are to be understood as forming a. part of this invention insofar as they fall within the true spirit and scope of the appended claim.

The invention is claimed as follows:

An electrical unit comprsing a relatively rigid core, an electrical element carried by said core, terminals connected to the ends of the electrical element, and a molded vitreous body of ceramic material covering the core and the electrical element, said molded vitreous body including initially substantial amounts of both glassy and non glassy ceramic particles with the glassy particles fused together as a glassy material envelope for the electrical unit having the non-glasy particles remaining embedded in the fused glassy material, said envelope being in intimate contact with exposed portions of said core and 'said electrical element.

References Cited by the Examier UNITED STATES PATENTS 4/1940 Morgan 338--264 X 2/ 1953 Berkelhamer 338-266 6/1958 Planer et al. 338-296 X 8/1959 Selsing 106-46 10/ 1959 Stetson 106-46 10/1960 Cianchi 317--258 8/1961 Cahill 338-264 X FOREIGN PATENTS 1/ 1947 Great Britain.

RICHARD M. WOOD, Primary Exam'er. 

